Turbo refrigerator

ABSTRACT

A turbo refrigerator includes a condenser that cools and liquefies a compressed refrigerant, an evaporator that vaporizes the liquefied refrigerant and takes away heat of vaporization from a cooling object, thereby cooling the cooling object, and a turbo compressor that compresses the refrigerant vaporized by the evaporator by rotation of an impeller driven to rotate by an electric motor, and supplies the compressed refrigerant to the condenser. Moreover, the turbo refrigerator includes a braking device that operates the electric motor as a generator when the impeller is urged to rotate by the vaporized refrigerant, so as to brake the rotation of the impeller.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a turbo refrigerator.

Priority is claimed on Japanese Patent Application No. 2010-092314,filed on Apr. 13, 2010, the content of which is incorporated herein byreference.

2. Description of Related Art

As a refrigerator that cools or freezes cooling objects such as water, aturbo refrigerator having a turbo compressor that compresses anddischarges a refrigerant in a gaseous state is known (for example, referto Japanese Patent Application, Publication No. 2007-177695). The turbocompressor compresses the refrigerant by the rotation of an impellerwhich is driven to rotate by an electric motor.

The refrigerant compressed by the turbo compressor is supplied to acondenser and then is cooled and liquefied. The liquefied refrigerant issupplied to an evaporator and is thus vaporized by the evaporator. Therefrigerant takes away heat of vaporization from a cooling object whenvaporized, thereby cooling the cooling object. The vaporized refrigerantis supplied to the turbo compressor again.

And now, when the turbo refrigerator is stopped (for example, at thetime of an emergency stop), the liquefied refrigerant which is stored inthe condenser vaporizes and flows back to the turbo compressor.Therefore, there is a possibility of the impeller of the turbocompressor being urged to reverse by the vaporized refrigerant. When theimpeller is reversed, there is a possibility of the turbo compressorbreaking down due to vibration or the like caused by the reversal. Inorder to prevent the reversal of the impeller, a configuration in whicha check valve is installed in the flow path between the condenser andthe turbo compressor to prevent a flow of the refrigerant toward theturbo compressor from the condenser, is generally used.

However, when the check valve is installed in the flow path, flowresistance against the refrigerant is increased, so that a pressure dropcaused by the flow of the refrigerant is increased. When the pressuredrop is increased, during normal operation, the freezing capability ofthe turbo refrigerator is degraded.

In consideration of the problem, an object of the invention is toprovide a turbo refrigerator capable of preventing or suppressingreversal of a turbo compressor, thereby reducing a pressure drop causedby the flow of the refrigerant.

SUMMARY OF THE INVENTION

In order to accomplish the object, the invention employs the followingmeans.

A turbo refrigerator related to the invention includes a condenser thatcools and liquefies a compressed refrigerant, an evaporator thatvaporizes the liquefied refrigerant and takes away the heat ofvaporization from a cooling object, thereby cooling the cooling object,and a turbo compressor that compresses the refrigerant vaporized by theevaporator by rotation of an impeller driven to rotate by an electricmotor, and supplies the compressed refrigerant to the condenser.Moreover, the turbo refrigerator related to the invention includes abraking device that operates the electric motor as a generator when theimpeller is urged to rotate by the vaporized refrigerant, so as to brakethe rotation of the impeller.

As described above, when the turbo refrigerator is stopped, theliquefied refrigerant stored in the condenser vaporizes and flows backto the turbo compressor. Therefore, there is a possibility of theimpeller of the turbo compressor being urged to reverse by the vaporizedrefrigerant. According to the invention, when the impeller is urged toreverse by the refrigerant, the braking device operates the electricmotor as a generator. When the electric motor is operated as agenerator, rotational resistance against the rotation of the impelleroccurs. Using the rotational resistance, the reversal of the impeller isbraked.

In addition, in the turbo refrigerator related to the invention, thebraking device may have a regeneration circuit that recovers electricalenergy generated by the electric motor.

In addition, in the turbo refrigerator related to the invention, thebraking device may have a resistance circuit that converts theelectrical energy generated by the electric motor into heat energy.

According to the invention, since the braking device operates theelectric motor as a generator, the reversal of the impeller is braked.Accordingly, the reversal of the turbo compressor can be prevented orsuppressed. Moreover, as the braking device is provided, the reversal ofthe turbo compressor is prevented or suppressed. Therefore, a checkvalve is excluded from the turbo refrigerator. Therefore, a pressuredrop caused by the flow of the refrigerant is suppressed to be low, sothat the freezing capability of the turbo refrigerator is enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a skeleton framework of a turborefrigerator according to an embodiment of the invention.

FIG. 2 is a block diagram showing an operation when the turborefrigerator is stopped according to the embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, exemplary embodiments of the invention will be describedwith reference to FIGS. 1 to 2. As well, in the drawings used for thefollowing description, in order to allow each member to have arecognizable size, the scale of each member is appropriately changed.

FIG. 1 is a block diagram showing a skeleton framework of a turborefrigerator 1 according to an embodiment of the invention.

The turbo refrigerator 1 according to this embodiment is installed, forexample, at a building, a factory, or the like in order to generatecooling water for air-conditioning. In addition, the turbo refrigerator1 in this embodiment includes a turbo compressor 2, an inverter 3(braking device), a condenser 4, and an evaporator 5.

The turbo compressor 2 is a member that compresses a refrigerant gas X1which is a refrigerant in a gaseous state to generate a compressedrefrigerant gas X2. A first flow path R1 through which the refrigerantgas X1 flows and a second flow path R2 through which the compressedrefrigerant gas X2 flows are connected to the turbo compressor 2. Theturbo compressor 2 includes an impeller 21 and a motor 22 (electricmotor).

The impeller 21 is an impeller used for compressing the refrigerant gasX1. The refrigerant gas X1 is introduced to the impeller 21 via anintake (not shown) formed in a rotation axis line direction (thrustdirection) of the impeller 21. The introduced refrigerant gas X1 is sentoutward in the radial direction by the rotating impeller 21. On theoutside of the impeller 21 in the radial direction, a diffuser and ascroll chamber (not shown) are formed. In addition, the refrigerant gasX1 is compressed as flowing inside the diffuser and the scroll chamber,thereby generating the compressed refrigerant gas X2. The first flowpath R1 is connected to the above-mentioned intake, and the second flowpath R2 is connected to the scroll chamber.

The motor 22 is a driving device for rotating the impeller 21. The motor22 is an AC electric motor (three phase type) that is driven as AC poweris supplied thereto. In addition, the rotational speed of the motor 22can be changed by adjusting the frequency of the supplied AC power. Themotor 22 is integrally connected to the impeller 21 via a rotation shaft23. The rotation shaft 23 is supported so as to be rotatable via arolling bearing (a ball bearing, a roller bearing, or the like) (notshown). Moreover, the rolling bearing is a member for ensuring smoothrotation of the rotation shaft 23 in either of the forward and reverserotation directions.

The inverter 3 is an electronic device which drives the motor 22 of theturbo compressor 2 and brakes the reversal (rotation in a directionopposite to rotation during a general cooling operation) of the impeller21. The inverter 3 is connected to a main power supply system P thatsupplies power for operating the turbo refrigerator 1 and the motor 22via the respective power supply lines. The inverter 3 includes a drivingcircuit 31 and a regeneration circuit 32. The driving circuit 31 and theregeneration circuit 32 have a configuration in which they are notsimultaneously operated and operations thereof are switched on the basisof a signal (for example, a signal indicating a stop (an emergency stopor the like) of the turbo refrigerator 1) input to the inverter 3.

The driving circuit 31 is a circuit for driving the motor 22 bysupplying the AC power to the motor 22 from the main power supply systemP. In addition, the driving circuit 31 can adjust the frequency of theAC power supplied to the motor 22. As the driving circuit 31 adjusts thefrequency of the AC power, the rotational speed of the motor 22 ischanged. In addition, the compression capability of the turbo compressor2 and the cooling capability of the turbo refrigerator 1 are adjusted.Moreover, the driving circuit 31 may also be a circuit that adjusts thevoltage as well as the frequency of the AC power.

The regeneration circuit 32 is a circuit that brakes the reversal of theimpeller 21 to prevent or suppress the reversal of the turbo compressor2. In addition, the regeneration circuit 32 is provided in parallel withthe driving circuit 31. The regeneration circuit 32 is a circuit foroperating the motor 22 as a generator when the motor 22 is reversed bythe reversal of the impeller 21. In addition, the regeneration circuit32 recovers electrical energy generated by the motor 22 which isoperated as a generator and supplies the electrical energy to the mainpower supply system P (regeneration operation). Moreover, aconfiguration in which the electrical energy recovered by theregeneration circuit 32 is stored in a storage batter or the like may beemployed. In addition, the regeneration circuit 32 is configured as abraking device separately from the inverter 3 so as to be installed inparallel with the inverter 3.

The condenser 4 is a heat exchanger that cools and liquefies thecompressed refrigerant gas X2 to generate a refrigerant liquid X3. Thesecond flow path R2 through which the compressed refrigerant gas X2flows and a third flow path R3 through which the refrigerant liquid X3flows are connected to the condenser 4. Moreover, in the third flow pathR3, an expansion valve 6 for reducing the pressure of the refrigerantliquid X3 is installed.

The evaporator 5 is a heat exchanger that takes away heat ofvaporization from a cooling object such as water or the like byvaporizing the refrigerant liquid X3 for cooling the cooling object.Moreover, the refrigerant liquid X3 vaporized by the evaporator 5 ischanged into the refrigerant gas X1. The third flow path R3 throughwhich the refrigerant liquid X3 flows and the first flow path R1 throughwhich the refrigerant gas X1 flows are connected to the evaporator 5.

In the turbo refrigerator 1, the first flow path R1, the second flowpath R2, and the third flow path R3 form circulation flow paths of therefrigerant (the refrigerant gas X1, the compressed refrigerant gas X2,and the refrigerant liquid X3).

Next, a freezing operation of the turbo refrigerator 1 will be describedwith reference to FIG. 1.

The driving circuit 31 of the inverter 3 supplies the AC power to themotor 22 of the turbo compressor 2 from the main power supply system P.The motor 22 is driven as the AC power is supplied, and the impeller 21connected thereto via the rotation shaft 23 is rotated. As the impeller21 is rotated, the refrigerant gas X1 inside the first flow path R1 issucked to be introduced to the impeller 21. The introduced refrigerantgas X1 is sent outward in the radial direction of the impeller 21 andthen is compressed by flowing into the diffuser and the scroll chamber(not shown), and is thus changed into the compressed refrigerant gas X2.The compressed refrigerant gas X2 is sent to the second flow path R2connected to the scroll chamber.

The compressed refrigerant gas X2 is introduced to the condenser 4 viathe second flow path R2. The compressed refrigerant gas X2 is cooled andliquefied by the condenser 4 so as to be changed into the refrigerantliquid X3. The refrigerant liquid X3 is sent to the third flow path R3and is decompressed by the expansion valve 6.

The refrigerant liquid X3 decompressed by the expansion valve 6 isintroduced to the evaporator 5. The refrigerant liquid X3 is vaporizedby the evaporator 5, and thus the refrigerator X3 takes away heat ofvaporization from the cooling object such as water or the like, therebycooling the cooling object. When the refrigerant liquid X3 is vaporized,the refrigerant liquid X3 is changed into the refrigerant gas X1, andthe refrigerant gas X1 is sent to the first flow path R1. Therefrigerant gas X1 is introduced again to the turbo compressor 2 via thefirst flow path R1.

As such, the freezing operation of the turbo refrigerator 1 iscompleted.

Subsequently, an operation performed when the turbo refrigerator 1 isstopped is described with reference to FIG. 2. FIG. 2 is a block diagramshowing an operation performed when the turbo refrigerator 1 is stoppedaccording to this embodiment.

For example, a situation in which a device included in the turborefrigerator 1 has a problem and the turbo refrigerator 1 is stopped inan emergency will be described. When the turbo refrigerator 1 is stoppedin an emergency, a signal indicating an emergency stop is input to theinverter 3. In addition, the driving circuit 31 of the inverter 3 stopssupplying the AC power, so that the driving of the motor 22 is stopped.As the motor 22 is stopped, the rotation of the impeller 21 is stopped,so that discharge of the compressed refrigerant gas X2 to the secondflow path R2 is stopped. Therefore, the introduction of the compressedrefrigerant gas X2 to the condenser 4 is stopped.

As the introduction of the compressed refrigerant gas X2 to thecondenser 4 is stopped, the refrigerant liquid X3 stored in thecondenser 4 vaporizes and flows back to the second flow path R2. Aswell, the refrigerant gas produced by vaporization of the refrigerantliquid X3 tries to flow into the third flow path R3. However, since theflow resistance of the expansion valve 6 installed in the third flowpath R3 is high, the refrigerant gas produced by vaporization of therefrigerant liquid X3 mostly flows into the second flow path R2 and ischanged into a backflow refrigerant gas X4.

The backflow refrigerant gas X4 flows through the second flow path R2toward the turbo compressor 2 and is introduced to the turbo compressor2. The backflow refrigerant gas X4 is introduced to the impeller 21 fromthe outside thereof in the radial direction via the scroll chamber andthe diffuser (not shown) of the turbo compressor 2. The backflowrefrigerant gas X4 introduced to the impeller 21 causes the impeller 21to be urged to reverse. Here, the rotation shaft 23 is supported via therolling bearing (not shown), and the rolling bearing smoothly rotatesthe rotation shaft 23 in either of the forward and reverse rotationdirections. Therefore, the rotation shaft 23 connected to the impeller21 is smoothly reversed. Therefore, the motor 22 connected to theimpeller 21 via the rotation shaft 23 is also reversed.

On the other hand, as the signal indicating an emergency stop is inputto the inverter 3, the regeneration circuit 32 is operated instead ofthe driving circuit 31. The regeneration circuit 32 operates the motor22 as a generator.

That is, when the impeller 21 is urged to reverse by the backflowrefrigerant gas X4, the regeneration circuit 32 operates the motor 22 asa generator. When the motor 22 is operated as a generator, rotationalresistance against the reversal of the impeller 21 occurs. In addition,as the rotational resistance occurs, the reversal of the impeller 21 isbraked. When the urging force caused by the flow of the backflowrefrigerant gas X4 is smaller than the rotational resistance against theimpeller 21 caused by the motor 22, the reversal of the impeller 21 isstopped. In addition, when the urging force caused by the flow of thebackflow refrigerant gas X4 is larger than the rotational resistance,the reversal of the impeller 21 is suppressed. As a result, the reversalof the turbo compressor 2 is prevented or suppressed, so that vibrationor the like caused by the reversal is prevented, thereby preventingproblems such as a breakdown of the turbo compressor 2 or noise.

When the impeller 21 is reversed as being urged by the backflowrefrigerant gas X4, the motor 22 that is operated as a generatorgenerates electrical energy. The regeneration circuit 32 recovers theelectrical energy generated by the motor 22 and supplies the electricalenergy to the main power supply system P. That is, the flow energy ofthe backflow refrigerant gas X4 is reused.

As well, in this embodiment, the inverter 3 has the regeneration circuit32. However, instead of the regeneration circuit 32, the inverter 3 mayhave a resistance circuit. The resistance circuit is a circuit thatoperates the motor 22 as a generator when the impeller 21 is reversedand converts electrical energy generated by the motor 22 into heatenergy. The regeneration circuit 32 supplies the electrical energygenerated by the motor 22 to the main power supply system P. However,when the voltage generated by the motor 22 is lower than the voltage inthe main power supply system P, the electrical energy generated by themotor 22 cannot be supplied to the main power supply system P(cancellation of regeneration). When cancellation of regenerationoccurs, the rotational resistance against the impeller 21 insufficientlyoccurs. Therefore, it is possible to obtain a stable braking operationby using the resistance circuit. As well, when the resistance circuit isused, the electrical energy is converted into heat energy and isdissipated. In addition, a configuration in which the inverter 3 hasboth the regeneration circuit 32 and the resistance circuit and selectsan operating circuit from the regeneration circuit 32 and the resistancecircuit in response to the voltage generated by the motor 22 may also beemployed.

As such, the operation performed when the turbo refrigerator 1 isstopped is completed.

As described above, the inverter 3 according to this embodiment has theregeneration circuit 32. Accordingly, the reversal of the impeller 21 isbraked, so that the reversal of the turbo compressor 2 is prevented orsuppressed. Therefore, the check valve installed in the second flow pathR2 to prevent the flow of the backflow refrigerant gas X4 is excludedfrom the turbo refrigerator 1. As the check valve is excluded from thesecond flow path R2, the flow resistance of the second flow path R2itself is reduced, so that a pressure drop that occurs when thecompressed refrigerant gas X2 flows through the second flow path R2 issuppressed to be low. As the pressure drop caused by the flow of thecompressed refrigerant gas X2 is suppressed to be low, the freezingcapability of the turbo refrigerator 1 is enhanced.

Therefore, according to this embodiment, the following effects can beobtained.

According to this embodiment, as the inverter 3 operates the motor 22 asa generator, the rotation of the impeller 21 is braked. Therefore, thereversal of the turbo compressor 2 is prevented or suppressed. As theinverter 3 is provided, the reversal of the turbo compressor 2 isprevented or suppressed. Therefore, the check valve is excluded from theturbo refrigerator 1. Therefore, the pressure drop caused by the flow ofthe compressed refrigerant gas X2 is suppressed to be low, so that thefreezing capability of the turbo refrigerator 1 is enhanced.

While the exemplary embodiments related to the invention have beendescribed with reference to the accompanying drawings, the invention isnot limited to the related embodiments. The shapes and combinations ofthe constituent members described in the above embodiments are onlyexamples and can be modified in various manners depending on designrequirements without departing from the spirit and scope of theinvention.

For example, in the above embodiments, the turbo compressor 2 is asingle-stage compressor having only the impeller 21. However, theinvention is not limited to this configuration, and a multi-stagecompressor having a plurality of impellers may also be employed.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

1. A turbo refrigerator comprising: a condenser that cools and liquefiesa compressed refrigerant; an evaporator that vaporizes the liquefiedrefrigerant and takes away heat of vaporization from a cooling object,thereby cooling the cooling object; a turbo compressor that compressesthe refrigerant vaporized by the evaporator by rotation of an impellerdriven to rotate by an electric motor, and supplies the compressedrefrigerant to the condenser; and a braking device that operates theelectric motor as a generator when the impeller is urged to rotate bythe vaporized refrigerant, so as to brake the rotation of the impeller.2. The turbo refrigerator according to claim 1, wherein the brakingdevice has a regeneration circuit that recovers electrical energygenerated by the electric motor.
 3. The turbo refrigerator according toclaim 1, wherein the braking device has a resistance circuit thatconverts the electrical energy generated by the electric motor into heatenergy.
 4. The turbo refrigerator according to claim 2, wherein thebraking device has a resistance circuit that converts the electricalenergy generated by the electric motor into heat energy.